Ba–Mg Dual-Metal–Boronitride Solvent for High-Yield and High-Quality Hexagonal Boron Nitride Single Crystals

High-crystallization and high-purity hexagonal boron nitride (h-BN) single crystals (SCs) obtained under high-pressure and high-temperature (HPHT) conditions have been used as an essential substrate or encapsulation material for two-dimensional (2D) van der Waals heterostructures. However, the classical Ba-solvent-based HPHT synthesis shows low production yield and is not fitting to the increasing demand powered by the prosperity of the 2D community. In this study, we reported a Ba–Mg dual-metal–boronitride (DMB) based solvent that significantly enhances the yield of HPHT h-BN SCs, with further enhanced crystal quality. Ba–Mg DMB shows 4.8-times yield increasing, achieving a stable yield of ∼57.3%, compared with a yield of ∼12% in Ba-based solvent. Magnesium element in the Ba–Mg DMB is found to act as an effective carbon and oxygen purifier under HPHT conditions, playing an essential role for obtaining the exceptionally high-quality h-BN SCs. The high quality of h-BN crystals is evidenced by detailed characterizations using Raman, X-ray diffraction, and X-ray photoelectron spectroscopy, especially the photoluminescence and cathodoluminescence. We further provide direct evidence that Ba–Mg DMB-derived h-BN SCs serve as an ideal encapsulation material for 2D-devices by demonstrating high carrier mobility in monolayer graphene. This study offers an effective route for the high-yield synthesis of high-quality HPHT h-BN SCs that work as a reliable material for high-performance 2D-devices.